Method for the formation of paint films and the paint films

ABSTRACT

A method for the formation of a paint film in which an aluminum or aluminum alloy part is subjected to an anodic oxidation treatment and an anodic oxide film is formed on the surface of the aluminum or aluminum alloy part, an anti-rust primer is coated on said anodic oxide film and an anti-rust primer paint film is formed and, as required, a top-coat paint is coated on said anti-rust primer paint film and a top-coat paint film is formed in which said anti-rust primer includes a base resin comprising hydroxyl group containing epoxy resin and a hardening agent, selected from among melamine resin and polyisocyanate, and barium sulfate, and the proportion of said barium sulfate included is a proportion within the range from 20 to 70 parts by mass per 100 parts by mass in total of the solid fractions of the base resin and the hardening agent.

TECHNICAL FIELD

The present invention concerns a method with which paint films are formed on the surface of aluminum or aluminum alloy parts and the paint films obtained with this method of forming paint films.

Aluminum and aluminum alloys have been used for some parts of outboard motors and the like and in recent years they have been used for automobile parts with a view to reducing the weight of automobiles.

The aluminum and aluminum alloy parts for outboard motors form part of the engine and drive system which is the power source for the boat and a high degree of corrosion resistance is required to protect the engine from heat, water, seawater, light and the like.

Furthermore, the aluminum and aluminum alloy parts used in automobiles also require a high level of corrosion resistance in view of the effects of snow-melting agents and the like.

Methods in which an epoxy resin paint or the like which includes a chromium-based anti-rust pigment is coated as an anti-rust primer have been widely used as methods of raising the corrosion resistance of aluminum and aluminum alloys, but the chromium-based anti-rust pigments contain chromium which presents the risk of having an adverse effect on the environment and so methods of applying anti-rust primers which contain chromium-free anti-rust pigments have been developed.

However, there is a problem with methods of applying anti-rust primers which contain chromium-free anti-rust pigments in that the corrosion resistance is poor when compared with that of the methods in which anti-rust primers which contain chromium-based pigments are applied.

On the other hand, methods in which the surface of an aluminum or aluminum alloy part is subjected to an anodic oxidation treatment are also widely used as a method of raising the corrosion resistance of aluminum and aluminum alloy parts, but the corrosion resistance with just an anodic oxidation treatment is unsatisfactory and a hole-sealing treatment is carried out after the anodic oxidation treatment (see, for example, Patent Citation 1).

However, although the corrosion resistance is improved when a hole-sealing treatment is carried out after an anodic oxidation treatment there is a problem in that the adhesion between the anodic oxide film which has been formed on the surface of the aluminum or aluminum alloy part by the anodic oxidation treatment and the paint film which is formed over the top is reduced. It is thought that this problem is caused by the hole-sealing treatment which is carried out after the anodic oxidation treatment and by the dissolving out of film and sealing treatment components in the de-greasing treatments and chemical forming treatments which are carried out subsequently, depending on the particular case.

On the other hand, corrosion preventing paint compositions for ships comprising optically transparent inorganic fillers, selected from among talc, mica, silica, potassium feldspar and barium sulfate; epoxy resin; and epoxy resin hardening agent, such as polyamide or polyamine, are known as corrosion preventing paints for ships which have corrosion resistance (for example, see Patent Citation 2). However, when these paint compositions are coated on the anodic oxide films of aluminum and aluminum alloy parts the corrosion resistance of the paint films which are obtained is inadequate.

Furthermore, coating a thermosetting type aqueous paint composition which includes barium sulfate or talc as a true pigment on metal materials which have been treated with a phosphate chemical forming solution of pH from 2.5 to 3.5 which contains phosphate ions, chlorate ions, nitrate ions, bromate ions and from 200 to 800 ppm of zirconium hexafluoride ions is known as a method for improving the corrosion resistance of metal materials (for example, see Patent Citation 3). However, when these thermosetting type aqueous paint compositions are coated on the anodic oxide films of aluminum or aluminum alloy parts the corrosion resistance of the paint films obtained is inadequate.

Furthermore, thermosetting type paints which are characterized in that they contain barium sulfate and calcium carbonate and in that they contain from 30 to 45 wt % alkyd resin, from 5 to 20 wt % melamine resin and from 0.2 to 1.5 parts by weight of anti-rust pigment and epoxy resin are known as thermosetting type paints which can be used for coating metal parts such as acid washed steel sheet and SPCC materials and the like to form coated materials with which thick paint films which provide both anti-rust performance and an excellent appearance can be formed, and which can be coated as an undercoat, mid-coat and top coat with a single application (for example, see Patent Citation 4). However, when these thermosetting type paints are coated on the anodic oxide films of aluminum and aluminum alloy parts the corrosion resistance of the paint films obtained is inadequate.

Furthermore, paints for metals such as zinc-plated steel sheet and the like which are characterized in that they include (A) a synthetic resin component comprising one type, or two or more types, selected from among (meth)acrylic acid ester resin-based emulsion, styrene/acrylic acid ester copolymer emulsion, vinyl acetate resin-based emulsion, vinyl acetate/(meth)acrylic acid ester copolymer emulsion, urethane resin-based emulsion, ethylene/vinyl acetate copolymer emulsion, polyester resin and aqueous epoxy resin, (B) a filler component comprising one type, or two or more types, selected from among titanium oxide, talc, kaolin, bentonite, mica, silica, heavy calcium carbonate, clay, precipitated barium sulfate, barium carbonate, glass beads and resin beads, and a mixed component of (C-1) from 10 to 95 mass % of specified acetylene glycol and/or epoxidized specified acetylene glycol and (C-2) from 5 to 90 mass % polyoxy-(ethylene•propylene) block polymer are known (see, for example, Patent Citation 5). However, when these paint compositions for metals are coated on the anodic oxide films of aluminum or aluminum alloy parts the corrosion resistance of the paint films obtained is inadequate.

Furthermore, a thermosetting type aqueous composition for metal coating purposes which is characterized in that it includes, as essential film forming components, (a) a modified epoxy resin which has been obtained by reacting an epoxy resin with at least one type of carboxylic acid selected from among the group comprising saturated carboxylic acids or derivatives thereof; ethylenic unsaturated carboxylic acids or derivative thereof; carboxylic acids which have aromatic rings or derivatives thereof; and oxy-carboxylic acids or derivatives thereof and a compound which has at least two hydroxyl groups which are bound to a phosphorus atom in one molecule, (b) a water-soluble or water-dispersible resin, excluding the abovementioned modified epoxy resins (a), and (c) at least one type of curing agent selected from among the group comprising aminoplast resins; phenoplast resins and blocked isocyanate resins are known as thermosetting type aqueous compositions for metal coating purposes (for example, see Patent Citation 6). However, these thermosetting type aqueous compositions for metal coating purposes are such that under extreme immersion testing conditions the corrosion resistance of the paint films which are obtained is inadequate.

PRIOR ART LITERATURE Patent Citations Patent Citation 1:

-   Japanese Unexamined Patent Application Laid Open 2004-60044

Patent Citation 2:

-   Japanese Unexamined Patent Application Laid Open 2000-037658

Patent Citation 3:

-   Japanese Unexamined Patent Application Laid Open 2003-10774

Patent Citation 4:

-   Japanese Unexamined Patent Application Laid Open 2003-313492

Patent Citation 5:

-   Japanese Unexamined Patent Application Laid Open 2008-063472

Patent Citation 6:

-   Japanese Unexamined Patent Application Laid Open H08-325509

OUTLINE OF THE INVENTION Problems to be Resolved by the Invention

The present invention is intended to provide a method for the formation of a paint film with which the adhesion with an anodic oxide film which has been formed on the surface of an aluminum or aluminum alloy part of a paint film comprising an anti-rust primer paint film which has been formed on said anodic oxide film and a topcoat paint film, as required, is excellent and which has excellent corrosion resistance, and the paint films obtained with this method of forming a paint film.

Means of Resolving These Problems

The inventors have discovered that the abovementioned problems can be resolved by subjecting an aluminum or aluminum alloy part to an anodic oxidation treatment to form an anodic oxide film on the surface of the aluminum or aluminum alloy part and then applying successively a specified primer paint containing a specified amount of barium sulfate and top-coat paint, as required, to form a paint film, and the invention is based upon this discovery.

That is to say, the present invention provides a method for the formation of a paint film in which an aluminum or aluminum alloy part is subjected to an anodic oxidation treatment and an anodic oxide film is formed on the surface of the aluminum or aluminum alloy part, an anti-rust primer is coated on said anodic oxide film and an anti-rust primer paint film is formed and, as required, a top-coat paint is coated on said anti-rust primer paint film and a top-coat paint film is formed which is characterized in that said anti-rust primer includes a base resin comprising hydroxyl group containing epoxy resin and a hardening agent, selected from among melamine resin and polyisocyanate, and barium sulfate, and the proportion of said barium sulfate included is a proportion within the range from 20 to 70 parts by mass per 100 parts by mass in total of the solid fractions of the base resin and the hardening agent.

Furthermore, the present invention provides a method for the formation of a paint film in which, in the abovementioned method of forming a paint film, the anodic oxidation treatment is carried out in dilute sulfuric acid.

Furthermore, the present invention provides a method for the formation of a paint film in which, in the aforementioned method of forming a paint film, the anodic oxide film on which the aforementioned anti-rust primer is coated is subjected to a hole-sealing treatment.

Furthermore, the present invention provides the paint films which are obtained with any of the abovementioned methods of forming a paint film.

Effect of the Invention

With the paint films of this invention the adhesion between the anodic oxide film which has been formed on the surface of an aluminum or aluminum alloy part by subjecting the aluminum or aluminum alloy part to an anodic oxidation treatment and the paint film comprising an anti-rust primer paint film and top-coat paint, as required, which has been formed on said anodic oxide film is excellent and, moreover, the corrosion resistance is also excellent.

BRIEF EXPLANATION OF THE DRAWING

FIG. 1 is an outline drawing of an example of electrolysis apparatus which can be used for anodic oxidation treatment.

EMBODIMENT OF THE INVENTION

No particular limitation is imposed upon the aluminum or aluminum alloy part which is used in this invention and various types can be cited, and examples include die-cast aluminum ADC12 and ADC10, aluminum cast material AC and drawn aluminum materials.

Moreover, no particular limitation is imposed upon the type of components of the aluminum alloys and examples include aluminum/magnesium based alloys, aluminum/magnesium/silicon based alloys, aluminum/copper based alloys, aluminum/zinc/magnesium based alloys and the like.

No particular limitation is imposed upon the shape of the aluminum or aluminum alloy part and it may be of various shapes, for example it may have the shape of a sheet, a bar or the like.

In this invention the aluminum or aluminum alloy parts are subjected to an anodic oxidation treatment.

This anodic oxidation treatment is preferably carried out in a bath of dilute sulfuric acid, oxalic acid, phosphoric acid, chromic acid or the like, more desirably in a dilute sulfuric acid bath or an oxalic acid bath, and most desirably in a dilute sulfuric acid bath. Just one of these bath types can be used individually, or a mixture of two or more types can be used, but the use of one type alone is preferred.

The electrolyte concentration in each bath is preferably from 1 to 20 vol %, and most desirably from 2 to 15 vol %. The sulfuric acid concentration in a dilute sulfuric acid bath in particular is preferably from 6 to 14 vol %, and most desirably from 8 to 12 vol %.

The temperature of the anodic oxidation treatment generally is preferably from 1 to 40° C., more desirably from 5 to 30° C., and most desirably from 10 to 25° C.

The anodic oxidation treatment can be carried out using various types of apparatus. One example is shown in FIG. 1.

The apparatus shown in FIG. 1 is electrolysis apparatus for anodic oxidation treatment purposes which comprises an electrolysis tank 2, a pair of cathode plates 3, an anode power supply lead 4, a cathode power supply lead 5 and a power source 6, and it is such that the aluminum or aluminum alloy part 1 can be fitted. This electrolysis apparatus has the direct current power source 61 which carries out a direct current electrolysis treatment as a structural element, but the apparatus is not limited to a direct current power source and alternating current treatment in which an alternating current power source is used for the power source, and both alternating and direct current electrolysis treatment in which direct current and alternating current are combined can also be carried out.

In this invention the aluminum or aluminum alloy part is subjected to an anodic oxidation treatment and an anodic oxide film is formed on the surface of the aluminum or aluminum alloy part.

The anodic oxide film may be subjected to a hole-sealing treatment, and a degreasing treatment and/or chemical forming treatment may be carried out after this treatment.

The hole-sealing treatment can be carried out by immersion in a hole-sealing treatment agent bath which has a metal hydrate and metal oxide sol as the main component, by spray coating with a hole-sealing treatment agent which has a metal hydrate and metal oxide sol as the main component, with an electrolytic treatment with a hole-sealing agent which has a metal hydrate and metal oxide sol as the main component or with a combination of these methods.

Examples of the metal of the metal hydrate and metal oxide sol include aluminum, silicon, zinc, tin, chromium, molybdenum, nickel, cobalt, copper, titanium, zirconium, yttrium, antimony, indium, calcium, germanium, strontium, vanadium, tantalum, neodymium, magnesium, barium and the like.

Furthermore, the hole-sealing treatment can also be carried out with the usual steam methods such as the pure water boiling method or the like.

Degreasing may be carried out with a known method such as immersion in the various types of degreasing agent for example. The known degreasing agents such as the alkali degreasing agents and the like can be used for the degreasing agent.

A chemical forming treatment can be carried out using the known methods such as immersion in the various types of chemical forming treatment agents. The known chemical forming treatment agents such as the chromium-based chemical forming agents and the like can be used for the chemical forming treatment agent.

The anodic oxide film is a film which includes aluminum oxide as the main component and it may be a film which includes the hydrate or hydrated oxide of a metal as a result of a hole-sealing treatment or a degreasing and/or chemical forming treatment.

No particular limitation is imposed upon the thickness of the anodic oxide film but generally it is of thickness preferably from 3 to 30 μm, more desirably of from 4 to 20 μm, and most desirably of from 5 to 18 μm.

In this invention an anti-rust primer is coated over the anodic oxide film which has been formed on the surface of the aluminum or aluminum alloy part and an anti-rust primer paint film is formed.

In this invention the anti-rust primer is an anti-rust primer which includes a base resin comprising hydroxyl group containing epoxy resin, a hardening agent selected from among melamine resin and polyisocyanate, and barium sulfate, and said barium sulfate content is from 20 to 70 parts by mass per 100 parts by mass in total of the solid fractions of the base resin and the hardening agent.

No particular limitation is imposed upon the hydroxyl group containing epoxy resin which is used for the base resin, and examples include the modified epoxy resins where epoxy resins obtained by forming bisphenol A, bisphenol F or a novolak or the like into glycidyl ethers have been modified with alkyd, polyester, polyether, acrylic or urethane or the like. One of these hydroxyl group containing epoxy resins can be used alone, or two or more types can also be used conjointly.

No particular limitation is imposed upon the hydroxyl group value of the hydroxyl group containing epoxy resin, but generally the value is preferably from 30 to 250 mgKOH/g, more desirably from 60 to 210 mgKOH/g, and most desirably from 90 to 190 mgKOH/g. If the hydroxyl group value of the hydroxyl group containing epoxy resin is less than 30 mgKOH/g then there are cases where corrosion resistance and adhesion are reduced. If it is greater than 250 mgKOH/g then there are cases where the water resistance is reduced.

No particular limitation is imposed upon the weight average molecular weight of the hydroxyl group containing epoxy resin, but generally it is preferably from 6,000 to 30,000, more desirably from 7,000 to 25,000, and most desirably from 9,000 to 20,000. If the weight average molecular weight of the hydroxyl group containing epoxy resin is less than 6,000 then there are cases where the corrosion resistance and adhesion are reduced. If it exceeds 30,000 then there are cases where the viscosity rises and it is difficult to form a paint. Moreover, in this invention the weight average molecular weight is the value of the average molecular weight measured using gel permeation chromatography (GPC) calculated on the basis of the average molecular weight of polystyrene.

Other base resins apart from the hydroxyl group containing epoxy resin may be included in the base resin within ranges where they do not overturn the aims of the invention. Examples of these other base resins include unmodified epoxy resins, alkyd resins, polyester resins, acrylic resins, urethane resins and the like. The proportion of other base resin included is preferably not more than 40 mass %, more desirably not more than 30 mass %, and most desirably not more than 20 mass % with respect to the whole of the base resin.

The melamine resins which are used as one type of hardening agent can be of various types provided that they function as hardening agents for the aforementioned epoxy resin. For example, methyl etherified melamine resins, butyl etherified melamine resins or mixed alkyl etherified melamine resins can be used for the aforementioned melamine resin. One of these melamine resins can be used alone, or two or more types can also be used conjointly.

The polyisocyanates which are used as one type of hardening agent can be of various types provided that they function as hardening agents for the aforementioned epoxy resin. For example, aliphatic polyisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate and the like or polymers of mixtures of these, alicyclic polyisocyanates such as 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate, isophorone diisocyanate and the like or polymers of mixtures of these, and aromatic polyisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4-diphenylmethane diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate and the like or polymers of mixtures of these can be cited as examples of the aforementioned polyisocyanates.

The proportions of base resin and hardening agent included may be the usual proportions, and when the hardening agent is a melamine resin the ratio by mass of the solid fractions of base resin and melamine resin is preferably from 50/50 to 90/10, more desirably from 55/45 to 85/15, and most desirably from 60/40 to 80/20. If the ratio by mass as solid fraction of melamine resin is more than 50/50 then there are cases where adhesion and paint stability are reduced. If the ratio is less than 90/10 then there are cases where corrosion resistance and adhesion are reduced. When the hardening agent is a polyisocyanate the mol ratio of base resin functional groups and polyisocyanate isocyanate groups is preferably from 3:1 to 1:3 and most desirably from 1.5:1 to 1:2. If the mol ratio of polyisocyanate isocyanate groups is less than 3:1 there are case where corrosion resistance is reduced, and if it is more than 1:3 there are cases where adhesion is reduced.

No particular limitation is imposed upon the barium sulfate which is used in the anti-rust primer and commercial products such as Barium Sulfate SS-50, Precipitated Barium Sulfate #100, Bariase B-30, Barifine BF-1, Barifine BF-10 and the like produced by the Sakai Kagaku Kogyo Co. can be cited as examples. The proportion of barium sulfate included in the anti-rust primer is from 20 to 70 parts by mass per 100 parts by mass in total of the solid fractions of the abovementioned base resin and the abovementioned hardening agent, but a proportion of from 25 to 60 parts by mass is preferred, and a proportion of from 30 to 45 mass % is most desirable. If the proportion of barium sulfate included is less than 20 parts by mass per 100 parts by mass in total of the solid fractions of the abovementioned base resin and the abovementioned hardening agent then the adhesion with aluminum or aluminum alloy parts is reduced and satisfactory corrosion resistance is not obtained. Furthermore, if the proportion of barium sulfate included exceeds 70 parts by mass per 100 parts by mass in total of the solid fractions of the abovementioned base resin and the abovementioned hardening agent then there are cases where the barium sulfate settles out and the stability of the anti-rust primer paint is reduced.

Furthermore, the anti-rust primer can include, as well as the abovementioned paint film forming resin and barium sulfate, anti-rust pigments, true pigments, coloring pigments, settling inhibitors, paint surface controlling agents, other additives used in paints, organic solvents and the like, as required, where the amounts included are within ranges such that there is no interference in practical terms.

No particular limitation is imposed upon the anti-rust pigments and examples include tetrabasic zinc chromate, basic zinc potassium chromate, strontium chromate, basic lead chromate, calcium chromate, barium chromate, lead suboxide, basic lead sulfate, calcium plumbate, lead cyanamide, zinc phosphate, calcium phosphate, magnesium phosphate, aluminum phosphate, magnesium tripolyphosphate, aluminum tripolyphosphate, aluminum calcium tripolyphosphate, zinc aluminum tripolyphosphate, zinc molybdate, calcium molybdate, zinc calcium molybdate, zinc phosphomolybdate, calcium phosphomolybdate, calcium phosphomolybdate, aluminum zinc phosphomolybdate and the like.

No particular limitation is imposed upon the true pigments and examples include hydrated aluminum silicate, hydrated magnesium silicate, silica powder and the like. The amount of said true pigment compounded is preferably not more than 40 parts by mass, and most desirably not more than 20 parts by mass, per 100 parts by mass of barium sulfate.

No particular limitation is imposed upon the coloring pigments and examples include inorganic pigments such as titanium oxide, carbon black, yellow iron oxide, bismuth vanadate, ultramarine and the like, and organic pigments such as the azo-based pigments, metal complex-based pigments, condensed polycyclic system-based pigment, phthalocyanine-based pigments and the like.

The anti-rust primer is preferably an organic solvent type anti-rust primer.

The various types of organic solvent which are generally used in paints can be used as the organic solvent which is used in a solvent type anti-rust primer, and examples include aromatic hydrocarbon based solvents, alicyclic hydrocarbon based solvents, ketone based solvents, alcohol based solvents, ester based solvents, ether based solvents, nitrogen containing solvents and the like, and an aromatic hydrocarbon based solvent, alcohol based solvent, ester based solvent or a mixture of two or more of these, for example, is preferred.

Preferred examples of the aromatic hydrocarbon based solvents include toluene, xylene, ethylbenzene, aromatic naphtha and the like. Preferred examples of the alicyclic hydrocarbon based solvents include cyclohexane, ethylcyclohexane and the like. Preferred examples of the ketone based solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone and the like. Preferred examples of the alcohol based solvents include methyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, 2-ethylhexyl alcohol and the like.

Preferred examples of the ester based solvents include aliphatic carboxylic acid alkyl esters such as ethyl acetate, n-butyl acetate, isobutyl acetate, ethyl propionate and the like, alkoxy aliphatic carboxylic acid esters such as 3-methoxybutyl acetate, ethyl 3-ethoxypropionate and the like, ethylene glycol aliphatic carboxylic acid esters such as cellosolve acetate and the like, and propylene glycol mono-alkyl ether aliphatic carboxylic acid esters such as propylene glycol mono-methyl ether acetate, propylene glycol mono-ethyl ether acetate, propylene glycol mono-propyl ether acetate and the like. Preferred examples of the ether based solvents include butyl cellosolve, dibutyl ether, tetrahydrofuran, 1,4-dioxane, 1,3,5-trioxane and the like. Preferred examples of the nitrogen-containing solvents include acetonitrile, valeronitrile, N,N-dimethylformamide, N,N-diethyl-formamide and the like. The organic solvent may be of one type alone, or it may be a mixture of two or more types.

The anti-rust primer is adjusted to the desired viscosity by heating or by adding an organic solvent or reactive diluent, as required, and then electrostatic coating or non-electrostatic coating is carried out using a painting machine of a type generally used, such as an air sprayer, airless sprayer or rotary atomization type painting machine or the like. From among these sprayer-painting is preferred.

Generally baking of the anti-rust primer paint film is desirable. The baking temperature should in general be selected appropriately from within the range from 80 to 160° C. Moreover in general the baking time should be selected appropriately within the range from 10 to 60 minutes. No particular limitation is imposed upon the thickness of the anti-rust primer paint film which is formed on applying the anti-rust primer but in general a dry film thickness of from 10 to 80 μm, more desirably of from 15 to 60 μm, and most desirably of from 20 to 40 μm is preferred.

In this invention the application of a top-coat paint over the anti-rust primer paint film to form a top-coat paint film is desirable.

No particular limitation is imposed upon the top-coat paint in this invention and the usual top-coat paints comprising paint film forming resin and hardening agent can be cited, and it may be a solid color paint or a metallic paint. A further top-coat paint may be coated over a paint film which has been formed by coating the aforementioned solid color paint or metallic paint, as required. The top-coat paint which is coated over a solid color paint film or metallic paint film may be a clear paint or a coloring paint in which a coloring agent such as a pigment or the like has been compounded.

Various resin-based paints can be used as solid color paints, and examples include acrylic/melamine based paints, alkyd/melamine based paints, polyester/melamine based paints, polyurethane based paints and the like. Furthermore, as with the solid color paints, acrylic/melamine based paints, alkyd/melamine based paints, polyester/melamine based paints, polyurethane based paints and the like can be cited as examples of the paints which can be used as metallic paints. Acrylic/melamine based paints, polyester/melamine based paints, polyurethane based paints, acid/epoxy based paints and the like can be cited as paints which can be used a clear paints and coloring paints.

The top-coat paint is adjusted to the desired viscosity by heating or by adding an organic solvent or reactive diluent, as required, and then electrostatic coating or non-electrostatic coating is carried out using a painting machine of a type generally used such as an air sprayer, airless sprayer or rotary atomization type painting machine or the like. From among these sprayer-painting is preferred.

In those cases where a clear paint or a coloring paint is coated over a solid color paint film or metallic paint film the clear paint or coloring paint may be coated after baking and hardening the solid color paint film or metallic paint film, or the clear paint or coloring paint may be applied wet-on-wet before baking the solid color paint film or coloring paint film and the two may be baked and hardened at the same time.

The baking temperature should in general be selected appropriately from within the range from 70 to 160° C. Moreover in general the baking time should be selected appropriately within the range from 10 to 60 minutes. No particular limitation is imposed upon the thickness of the top-coat paint film which is formed on coating a top-coat paint, but in general a dry film thickness of from 10 to 70 μm, and more desirably of from 15 to 50 μm, is preferred. Furthermore, in those cases where the top-coat paint film is a multiple-layer the thickness of each layer as the dry film thickness of each layer should be the thickness of the abovementioned top-coat paint film.

ILLUSTRATIVE EXAMPLES

Next the invention is described in more practical terms by means of illustrative examples, but the invention is not limited by these illustrative examples. Furthermore, in the illustrative examples the term “parts” signifies “parts by mass” in the absence of any indication to the contrary, and the term “%” in connection with amounts compounded and contents signifies “mass %”.

Examples of Anti-Rust Primer Production Production of Anti-Rust Primer Paint (PR-1)

After mixing pigments by formulating 21 parts of alkyd modified epoxy resin produced by BASF Coatings Japan Ltd. (hydroxyl group value 150 mgKOH/g, acid value 30 mgKOH/g, weight average molecular weight 18,000, solid fraction 60%, propylene glycol mono-methyl acetate and ethyl-3-ethoxypropionate mixed solution), 10 parts of barium sulfate (trade name SS-50, produced by the Sakai Kagaku Kogyo Co.), 4 parts of anti-rust pigment (trade name Strontium Chromate L203E, produced by the Societe Nouvelle des Couleurs Zinciques Co.), 0.3 part of black pigment (trade name Raben 1255, produced by the Columbia Carbon Co.), 10 parts of white pigment (trade name TiPure R-900, produced by the DuPont Co.), 0.3 part of additive (trade name Benton 34, produced by the Elementis Japan Co.) and 13.4 parts solvent and dispersing to less than 10 μm, the organic solvent type anti-rust primer paint PR-1 was produced by mixing with 10.5 parts of alkyd modified epoxy resin produced by BASF Coating Japan Ltd., 7 parts of epoxy resin (a 40 mass % solution in a mixture of xylene, butyl alcohol and propylene glycol mono-methyl ether acetate of trade name jER1009, produced by the Nippon Epoxy Resin Co.), 12 parts of melamine resin (trade name Yuban 225, 60 mass % solid fraction, produced by the Mitsui Kagaku Co.) and 11.5 parts of propylene glycol mono-methyl ether acetate, xylene, butyl alcohol mixed solvent.

Production of Anti-Rust Primer Paints (PR-2 to PR-11)

Anti-rust primers PR-2 to PR-11 were produced in the same way as anti-rust primer paint PR-1 using the various components presented in Table 1 and Table 2. However, with anti-rust primer PR-8 the solvent was changed to a toluene, propylene glycol mono-methyl ether acetate mixed solvent and the polyisocyanate compound (trade name Sumidure N-3300, produced by the Sumika Bayer Urethane Co.) which was the hardening agent of the anti-rust primer PR-8 was used by mixing immediately before use.

Furthermore, the stability of each of the anti-rust primer paints obtained was evaluated by means of the method indicated below.

Evaluation of the Stability of an Anti-Rust Primer Paint

The evaluation of the stability of an anti-rust primer paint was carried out by observing visually the state of the paint when it had been left to stand for 2 weeks at normal temperature and the evaluation was made on the basis of the criteria indicated below. The results obtained are shown in Table 1 and Table 2.

Paint Stability Evaluation Criteria

{circle around (⊙)}: No settling ◯: Slight settling but recovered easily on stirring Δ: Settling but recovered on stirring X: Settled. Did not recover even on stirring

TABLE 1 Amount Compounded (parts by mass) Composition PR-1 PR-2 PR-3 PR-4 PR-5 PR-6 Before Hydroxyl Group Alkyd Modified epoxy resin 21 21 21 21 21 21 Dispersion Containing Epoxy solution¹⁾ Resin Solution H201-60BT²⁾ Barium SS-50³⁾ 10 20 6 10 8 15 Sulfate B-30⁴⁾ Anti-rust L203E⁵⁾ 4 4 4 4 4 Pigment PM300C⁶⁾ 4 Black Pigment R1255⁷⁾ 0.3 0.3 0.3 0.3 0.3 0.3 White Pigment R-900⁸⁾ 10 12 10 10 5 True Hi·filer #12⁹⁾ 2 2 Pigment R972¹⁰⁾ Additive Benton 34¹¹⁾ 0.3 0.3 0.3 0.3 0.3 0.3 Solvent 13.4 13.4 13.4 13.4 13.4 13.4 After Hydroxyl Group Alkyd Modified epoxy resin 10.5 10.5 10.5 10.5 10.5 10.5 Dispersion Containing Epoxy solution Resin Solution H-201-60BT Epoxy Resin Solution jER1009 solution¹²⁾ 7 7 7 7 7 7 Melamine Resin U225¹³⁾ 12 12 12 12 12 12 Polyisocyanate N3300¹⁴⁾ Solvent 11.5 11.5 11.5 11.5 11.5 11.5 Total 100 100 100 100 100 100 Amount of Barium Sulfate Included with 36 69 21 35 28 52 respect to all of the resin mass % Stability of the Anti-rust Primer Paint

Δ

◯

TABLE 2 Amount Compounded (Parts by Mass) Composition PR-7 PR-8 PR-9 PR-10 PR-11 Hydroxyl Group Alkyd Modified epoxy resin solutions¹⁾ 21 21 21 18 Containing Epoxy H201-60BT²⁾ 24 Resin Solution Barium SS-50³⁾ 12 5 20 Sulfate B-30⁴⁾ 10 Anti-rust L203E⁵⁾ 4 4.5 4 4 4.3 Pigment PM300C⁶⁾ Black Pigment R1255⁷⁾ 0.3 0.3 0.3 0.3 0.2 White Pigment R-900⁸⁾ 10 7 13 10 6.7 True Hi·filer #12⁹⁾ 2 Pigment R972¹⁰⁾ 10 Additive Benton 34¹¹⁾ 0.3 0.3 0.3 0.3 0.3 Solvent 13.4 12 13.4 13.4 13.4 OH Group Cont. Alkyd Modified epoxy resin solution 10.5 10.5 10.5 10.5 Epoxy Resin Solution H-201-60BT 15 Epoxy Resin Solution jER1009 solution¹²⁾ 7 7 7 6.5 Melamine Resin U225¹³⁾ 12 12 12 11 Polyisocyanate N3300¹⁴⁾ 14.3 Solvent 11.5 10.6 11.5 11.5 9.1 Total 100 100 100 100 100 Amount of Barium Sulfate Included with 35 32 17 0 76 respect to all of the resin mass % Stability of the Anti-rust Primer Paint

X

Explanation of Table 1 and Table 2

Each superscript number in the tables has the significance indicated below.

1) Alkyd modified epoxy resin solution: Produced by BASF Coatings Japan Ltd., solid fraction 60 mass %, hydroxyl group value 150 mgKOH/g, weight average molecular weight 18,000 2) H201-60BT: Polyol type epoxy resin, solid fraction mass %, hydroxyl group value 120 mgKOH/g, weight average molecular weight 10,000, toluene, methyl isobutyl ketone mixed solution, trade name Epicron H201-60BT, produced by the DIC Co. 3) SS-50: Barium sulfate, trade name SS-50, produced by the Sakai Kagaku Kogyo Co. 4) B-30: Barium sulfate, trade name B-30, produced by the Sakai Kagaku Kogyo Co. 5) L203E: Strontium chromate, trade name Strontium Chromate L203E, produced by the Societe Nouvelle des Couleurs Zinciques Co. 6) PM300C: Aluminum zinc phosphomolybdate, trade name LF Bosei PM300C, produced by the Kikuchi Color Co. 7) R1255: Carbon black, trade name Raben 1255, produced by the Columbia Carbon Co. 8) R-900: Titanium oxide, trade name TiPure R-900, produced by the DuPont Co. 9) Hi•Filler #12: Talc, trade name Hi•filler #12, produced by the Matsumura Sangyo Co. 10) R972: Silica, trade name Aerosil R972, produced by the Nippon Aerosil Co. 11) Benton 34: Tetra-alkylammonium bentonite, trade name Benton 34, produced by the Elementis Japan Co. 12) jER1009 solution: A 40 mass % xylene, butyl alcohol, propylene glycol mono-methyl ether acetate mixed solution of epoxy resin, trade name jER1009, produced by the Japan Epoxy Resin Co.13) U225: Butylated melamine resin, solid fraction 60%, xylene, methyl alcohol, butyl alcohol mixed solution, trade name Yuban 225, produced by the Mitsui Kagaku Co. 14) N3300: Hexamethylene diisocyanate (HDI) isocyanurate, NCO group content 21.8 mass %, solid fraction 100 mass %, trade name Sumidure N-3300, produced by the Sumika Bayer Urethane Co.

Examples of Anodic Oxide Film Treatment Preparation of Anodic Oxide Film Treated Aluminum Alloy Part (AL-1)

An outboard motor part (gear case, 240×265×100 mm) comprising ADC12 material was subjected to anodic oxidation using the electrolysis apparatus for anodic oxidation treatment shown in FIG. 1 with the direct current electrolysis method when immersed in a treatment bath at 20° C. which had been filled with vol % sulfuric acid and an anodic oxide film of from 13 to 15 μm was formed. A direct current voltage of 35 V was applied and maintained for 15 minutes in the treatment bath to carry out the anodic oxidation treatment. Subsequently the part was immersed for minutes in a solution at 90° C. in which a commercial hole-sealing agent (product name: Topseal) had been dissolved and a hole sealing treatment was carried out, and then the part was rinsed with water and dried.

Preparation of Anodic Oxidation Film Treated Aluminum Alloy Part (AL-2)

An outboard motor part (housing) comprising AC4B material was subjected to anodic oxidation using the electrolysis apparatus for anodic oxidation treatment shown in FIG. 1 with the direct current electrolysis method when immersed in a treatment bath at 20° C. which had been filled with 10 vol % sulfuric acid and anodic oxide film of from 13 to 15 μm was formed. A direct current voltage of 35 V was applied and maintained for minutes in the treatment bath to carry out the anodic oxidation treatment. Subsequently the part was immersed for 15 minutes in a solution at 90° C. in which a commercial hole-sealing agent (product name: Topseal) had been dissolved and a hole sealing treatment was carried out, and then the part was rinsed with water and dried.

Preparation of Anodic Oxidation Film Treated Aluminum Alloy Part (AL-3)

An automobile part (lower case) comprising drawn aluminum material was subjected to anodic oxidation using the electrolysis apparatus for anodic oxidation treatment shown in FIG. 1 with the direct current electrolysis method when immersed in a treatment bath at 30° C. which had been filled with 3 vol % oxalic acid aqueous solution and a film of from about 15 μm was formed. A direct current voltage of 30 V was applied and maintained for 20 minutes in the treatment bath to carry out the anodic oxidation treatment. Subsequently a hole sealing treatment was carried out with the pure water boiling water method which is the usual steam method and the part was rinsed with water and dried.

Example 1

The anti-rust primer PR-1 was mixed with a propylene glycol mono-methyl ether acetate, xylene, butyl alcohol mixed solvent and spray painted over the anodic oxide film of the aluminum alloy part AL-1 which had been subjected to an anodic oxidation treatment in such a way that the dry film thickness was 25 μm and an anti-rust primer film was formed, and this was baked for 20 minutes at 130° C. Next hardening agent and diluent thinner were mixed immediately before use with a polyurethane resin based metallic paint (Hiurethane No. 5000 OEP, produced by the BASF Coatings Japan Ltd.) and spray painted as a metallic paint in such a way as to provide a dry film thickness of 15 μm over the anti-rust primer paint film to form a metallic paint film layer, and a urethane resin based clear paint (Hiurethane No. 5300 Clear for Outboard Motor Purposes, produced by BASF Coatings Japan Ltd.) was mixed with hardening agent and diluent thinner immediately before use and spray painted wet-on-wet on the metallic paint film in such a way as to provide a dry film thickness of 25 μm and a clear paint film was formed and, after being left to stand for 10 minutes at room temperature, the part was baked for 20 minutes at 90° C.

Crosscuts were made on the test product which had been produced in this way and after carrying out immersion tests of 1 hour at 80° C., and 240 hours at 40° C., (JIS Specification K5600-6-2) the corrosion resistance was evaluated by tape peeling. The results showed high adhesion with no peeling with at least 20 mass % barium sulfate.

Example 2

The anti-rust primer PR-8 was mixed with a toluene, propylene glycol mono-methyl ether acetate mixed solvent and spray painted on the aluminum alloy part AL-1 which had been subjected to an anodic oxidation treatment in such a way that the dry film thickness was 20 μm and an anti-rust primer film was formed, and hardening agent and diluent thinner were mixed immediately before use with a polyurethane resin based metallic paint (Hiurethane No. 5000 OEP, produced by the BASF Coatings Japan Ltd.) and spray painted wet-on-wet over the anti-rust primer paint film as a metallic paint in such a way as to provide a dry film thickness of 15 μm to form a metallic paint film layer, and a urethane resin based clear paint (Hiurethane No. 5300 Clear for Outboard Motor Purposes, produced by BASF Coatings Japan Ltd.) was mixed with hardening agent and diluent thinner immediately before use and spray painted wet-on-wet on the metallic paint film in such a way as to provide a dry film thickness of 25 μm and a clear paint film was formed and, after being left to stand for 10 minutes at room temperature, the part was baked for 20 minutes at 90° C. The result of immersion tests carried out in the same way as in Example 1 with test products which had been produced in this way showed high adhesion with no peeling.

Examples 3 to 10 and Comparative Examples 1 and 2

The test products of Examples 3 to 10 and Comparative Examples 1 and 2 were prepared in the same way as in Example 1 except for the part which had been subjected to an anodic oxidation treatment and that the composition of the anti-rust primer was set to the paint shown in Table 1, and immersion tests were carried out in the same way as in Example 1.

Examples 11 and 12

Example 11 was basically the same as the test product prepared in Example 1 but differed in that de-greasing was carried out after the anodic oxidation treatment. The degreasing conditions were 6 minutes at 60° C. using an alkali degreasing agent.

Furthermore, Example 12 differed from Example 1 in that it was degreased and then subjected to a chemical forming treatment. The degreasing conditions were 6 minutes at 60° C. using an alkali degreasing agent and the chemical forming treatment was a 3 minute treatment at 45° C. using a chromium-based chemical forming treatment agent. After preparation, the test products were subjected to immersion tests in the same way as in Example 1 and the results showed high adhesion with no peeling.

The results of the immersion tests of Examples 1 to 12 are shown in Tables 3 and 4, and the results of the immersion tests of Comparative Examples 1 and 2 are shown in Table 5.

The adhesion after the immersion test was evaluated using the method outlined below.

Adhesion After the Immersion Test

The adhesion after the immersion test was evaluated in accordance with the evaluation criteria indicated below.

{circle around (⊙)}: No peeling from the crosscut part at all on peeling off the tape ◯: Less than 2 mm of peeling from the crosscut part on peeling the tape. X: 2 mm or more of peeling from the crosscut part on peeling the tape.

TABLE 3 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Test Product AL-1 AL-1 AL-1 AL-1 AL-1 AL-1 Anti-rust Primer PR-1 PR-8 PR-2 PR-3 PR-4 PR-5 Adhesion 80° C.,

◯

After the  1 hour Immersion 40° C.,

◯

Test 240 hour

TABLE 4 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Test Product AL-1 AL-1 AL-2 AL-3 AL-1 AL-1 Anti-rust Primer PR-6 PR-7 PR-1 PR-1 PR-1 PR-1 Adhesion 80° C.,

After the  1 hour Immersion 40° C.,

Test 240 hour

TABLE 5 Comp. Ex. 1 Comp. Ex. 2 Test Product AL-1 AL-1 Anti-rust Primer PR-9 PR-10 Adhesion After the 80° C., 1 hour X X Immersion Test 40° C., 240 hour X X

[Potential for Industrial Use]

The coated aluminum or aluminum alloy parts where a paint film of this invention has been formed on the surface can be used in various fields such as parts for outboard motors and the like, automobile parts and the like.

KEY FOR THE DRAWING

-   1 Aluminum or aluminum alloy part -   2 Electrolysis tank -   3 Cathode plate -   4 Anode power supply lead -   5 Cathode power supply lead -   6 Power source -   61 Direct current power source 

1. A method for the formation of a paint film, comprising subjecting a part selected from the group consisting of an aluminum part and an aluminum alloy part, is subjected to an anodic oxidation treatment so as to form an anodic oxide film on the surface of the part, coating an anti-rust primer on said anodic oxide film so as to form an anti-rust primer paint film, and optionally coating a top-coat paint on said anti-rust primer paint film so as to form a top-coat paint film, wherein the anti-rust primer comprises a base resin comprising a hydroxyl group containing epoxy resin, a hardening agent selected from the group consisting of melamine resin and polyisocyanate, and barium sulfate, wherein the proportion of said barium sulfate included is a proportion within the range from 20 to 70 parts by mass per 100 parts by mass in total of the solid fractions of the base resin and the hardening agent.
 2. The method of claim 1 further comprising carrying out the aforementioned anodic oxidation treatment in a dilute sulfuric acid bath.
 3. The method of claim 2 further comprising subjecting the anodic oxide film on which the aforementioned anti-rust primer is coated to a hole-sealing treatment.
 4. A paint film obtained by the method for the formation of a paint film of claim
 1. 